Mach effect in presplitting

ABSTRACT

An improved method of presplitting is provided in which a high concentration of energy released upon detonation of a blasting charge in a blasting hole is focused along the desired presplit line. The focusing of the energy of detonation is achieved employing blasting charges having a configuration capable of producing a Mach Effect. Positioning of the blasting charges in the blasting holes permits the concentration of energy to be focused along the desired presplit line.

United States Patent Fritz 1451 Apr. 11, 1972 541 MACH EFFECT IN PRESPLITTING 3,349,705 10/1967 Wilson ..102/24 [72] inventor: Fred A. Fritz, Hockessin, Del. FO EIGN PATENTS O APPUCA-HONS 1 Assigneez Hercules Incorporated, Wilmington, 1391- 1,138,654 1/1969 Great Britain ..102/1)1c. 2

[22] filed: June 1970 Primary Examiner-Verlin R. Pendegrass [21] Appl. No.: 47,507 Attorney-S. Grant Stewart [52] U.S.Cl ..l02/23, 102/24 [57] ABSTRACT [51] Int. Cl .....F42d 1/04, F42d 3/04 An improved method of p p g is provided in which a [58] Field of Search ..102/22-24; 299/13 g concentration of energy released p detonation of a blasting charge in a blasting hole is focused along the desired [56] References Cited presplit line. The focusing of the energy of detonation is achieved employing blasting charges having a configuration UNITED STATES PATENTS capable of producing a Mach Effect. Positioning of the blasting charges in the blasting holes permits the concentration of 2,775,490 1/1957 Klotz ..102/23 t b f d t d d 3,021,785 2/1962 Hladel et a]. ..102/24 energy 0 e along he em presp me 3,076,408 2/1963 Poulter et al. ..102/23 10 Claims, 7 Drawing Figures PATENTED 11 I 2 3,654,866

FRED A FRITZ x INVENTOR 54 I i f f/ 4 I FIG. 5 BY fig/m AT TORNE Y PATENTEDAPR 11 I972 3.654666 sum 2 OF 2 FRED A. FRITZ INVENTOR BY 7zw/ bz/z' 15% AT T ORNE Y MACII EFFECT IN PRESPLITTING This invention relates to the use of the Mach Effect Effect in blasting operations and specifically to the use of the Mach Effect in presplitting. More particularly, this invention relates to a method of presplitting employing the Mach Effect to focus a high concentration of the energy of detonation of a blasting charge along a desired presplit line. In another aspect, this invention relates to a blasting system for establishing a shear plane in rock employing the focusing of energy of a blasting charge due to the Mach Effect.

Presplitting is a method of blasting in which a shear plane or break line sometimes referred to as a presplit crack, is

established in a rock formation to be blasted. This break line prevents over-break of the rock formation during subsequent blasting operations and reduces vibration of subseuqent blasting operations permitting blasting to be done close to buildings and utilities. Presplitting allows blasting of a smooth rock face at a predetermined alignment.

In conventional presplitting methods a blasting charge consisting of either incremental or continuous lengths of selected explosives is secured to adetonating cord. The detonating cord, having an explosive charge secured thereto and installed in a blasting hole, is referred to as a down-line. The free or upper end of the down-line generally is long enough to extend above the surface opening of the blast hole and is connected to a trunk line of detonating cord located on the surface on the formation along which a presplit is to be made. Detonation of the blasting charges results from initiation of the detonation of the detonating cord which detonates along its entire length and in turn initiates detonation of the blasting charges.

Detonation of a conventional blasting charge produces a detonation force pattern within each blasting hole which is approximately cylindrical. Although some alteration of this cylindrical symmetry of the detonation force pattern will occur withpropagation of the shock through the rock formation, the shock will arrive at the adjacent blasting hole having a substantially cylindrical force pattern. The cylindrical symmetry of this force pattern provides uniform stressing on the rock formation; a condition that is undesirable in presplitting. In presplitting, the force along the desired presplit line must be sufficient to properly couple the energy of the detonation to the rock formation in order for the presplit to occur. This same force, however, must be less than that required for radial fracturing of the rock formation. These force requirements define the boundary conditions of the energy requirements for presplitting. It therefore is highly desirable to control the concentration of the force of the detonation of a blasting charge in presplitting along the presplit line, rather than to stress the rock formation equally in all directions with the possibility of radial fracturing occuring.

The Mach Effect is the name given to a focusing action which occurs when two detonating shock fronts meet each other head-on producing a concentration of energy at right angles to the direction of the shock fronts. In the method of this invention, the focusing action of the Mach Efiect is employed to enhance and direct the energy of a blasting charge along a desired presplit line.

Broadly, in accordance with this invention the Mach Effect is employed to radially focus the energy of a detonation of a blasting charge along the entire length of the explosive charges in the blasting charge to improve efficiency in establishing a shear plane in rock. The blasting charge which is employed to achieve the Mach Effect comprises an explosive charge in the form of a cylinder or in the form of two cylinders of explosive secured together and being in a contiguous relationship lengthwise of said cylinders, and two detonating cords or fuses secured on the surface of the explosive charge and extending parallel to the longitudinal axis of the charge. These two detonating cords are spaced on opposite sides of the charge, 180 apart. The detonating cords are detonated simultaneously on the surface of the explosive charge. This simultaneous detonation of these cords produces the Mach Effect in release of the energy of detonation of the explosive charge.

The presplitting method of this invention comprises the steps of a) drilling a series of holes along a desired presplit line, b) charging the holes with a blasting charge as broadly defined above, C) positioning the blasting charges in each of the blast holes so that the energy released upon initiation of the blasting charges will be concentrated and focused and along the desired presplit line, and d) initiating detonation of said blasting charges to effect presplitting of the rock formation.

The following drawings will more fully illustrate this invention.

FIG. 1 is an elevational view of two blasting charges installed in two blasting holes, wherein the charges are designed and positioned for producing the Mach Effect along the desired presplit line.

FIG. 2 is a view along line 22 of FIG. 1.

FIG. 3 is a diagrammatic view illustrating the focusing action achieved when initiating the blasting charges of FIG. 1.

FIG. 4 is a top view of a blasting hole array as described in FIG. 1 in which the blasting charges are illustrated in section and are positioned so as to focus the blasting force along a desired presplit line.

FIG. 5 is a cross-sectional view of the second embodiment of a blasting charge which can be employed to achieve the Mach Effect in presplitting.

FIG. 6 illustrates a schematic view of a blasting hole array in a rock formation and the positioning of blasting charges in the holes to beneficially employ the Mach Effect wherein the desired presplit line is an arc of a circle.

FIG. 7 is a diagrammatic view illustrating positioning of blasting charges in blast holes so that substantial coincidence of force vectors (lines representing focusing of energy) with the desired presplit line is possible when the desired presplit line is the arc of a circle.

In FIG. 1 a blasting hole 10 is shown having a blasting charge 12 installed therein, the blasting charge being designed to exhibit the Mach Effect upon initiation of the charge. The blasting charge 12 comprises a series of cylindrical explosive charges 14a, b, c, d which are secured by any convenient means, such as taping, to two detonating cords 16, 17. The detonating cords are positioned apart on the surface of the charge as clearly illustrated in FIG. 2. The explosive charges 14 generally comprise a paper shell 20 filled with explosive 21. The detonating cord is contained within an encasement material 22 prepared from a textile or plastic material and contains an explosive charge 23. The free ends 24 a, 24 b of detonating cords l6 and 17 are connected at a common junction point to trunk line 18. Trunk line 18 is also prepared from detonating cord. The secured ends 26 a, 26 b of detonating cords l6 and 17 comprise any portion of the detonating cord which is either secured to an explosive charge or is in between or below a secured explosive charge in the blast hole. The end of trunk line 18 is connected to an electrical blasting cap 19. Electrical blasting cap 19 is connected through circuit 27 and open switch 28 to electrical power source 29. When open switch 28 is closed, current flows from power source 29 into blasting cap 19 detonating same, which detonation in turn detonates trunk line 18 and detonating cords l6 and 17. The lengths of detonating cords l6 and 17 are made equal so that simultaneous detonation of the cords occurs on opposite sides of the explosive charge producing the Mach Effect. By the term simultaneous detonation is meant that the detonation of the detonating cords occurs at substantially the same time.

The force vectors resulting from initiation of an explosive charge 14 illustrated as explosive charge 14 a, 14 b, 14 c or 14 d in FIG. 1 and as explosive charge 14 in FIG. 2 is shown diagrammatically in FIG. 3. Simultaneous detonation of detonating cords l6 and 17 produces detonating fronts 28 and 30 which detonate explosive charge 14 and which meet head-on producing the concentrated and focused force vectors 32 and 34 which occur at right angles to detonation fronts 30 and 31.

In FIG. 4 a top view of a series of blasting holes 36, 38, 40, 42 and 44 is shown. The blast holes are drilled in a straight line and each hole is. charged with a blasting charge 12 fully described and illustrated in FIGS. 1, 2, and 3. The desired presplit line or break line is shown as line 46. Each blasting charge 12 is positioned within blasting holes 36, 38, 40, 42 and 44 so that a line connecting the centers of detonating cords in each blasting hole, illustrated as line 48 connecting the centers of detonating cords l6 and 17 at blasting hole 36, is perpendicular to the desired presplit line 46.

In FIG. a second embodiment of a blasting charge is illustrated which will exhibit the Mach Effect upon initiation. This explosive charge is comprised of two cylindrical explosive cartridges 50 and 51 which are in a contiguous relationship lengthwise of said cylinders. Detonating cords 52 and 53 are each secured to and are disposed longitudinally on the surface of the explosive charge parallel to the longitudinal axis of the charge. These detonating cords 52, 53 are spaced 180 apart on the surface of the explosive charge at the points on the surface of the charge where a line, passing through the center of the explosive charge 54 and the centers of the cylindrical explosive cartridges 55, 56 forming the explosive charge, intersects the surface of the explosive charge.

FIG. 6 illustrates a schematic view of another arrangement of blasting holes in which the Mach Effect is employed to advantage in presplitting operations. In this arrangement blasting holes 58, 60, 62, 64, 66, 68, and 70 are spaced along an are 72 of a circle, which defines the desired presplit line. Each blasting hole has a blasting charge 12 contained therein. The blasting charges 12 are oriented within the holes so that the resultant force from simultaneous detonation of blasting cords 16 and 17 substantially coincides with the desired presplit line 72.

FIG. 7 further 74, 76 the orientation of blasting charges 12 in blast holes 74,76 and 78 drilled along the arc of a circle 80 in which the are 80 of the circle defines the desired presplit line. The force vectors from each charge 12 are shown by arrows extending outwardly from the blast holes at right angles to a line connecting the centers of detonating cords of the blasting charge in each blast hole 74, 76 and 78. The charges are positioned so that the force vectors will substantially coincide with or be as close to the arc of the circle as is possible over the distance of the arc so that an effective presplit is accomplished.

The following examples more fully illustrate the method of presplitting of this invention. Example 1 illustrates a conventional presplitting method.

EXAMPLE 1 Four blasting holes are drilled in a straight line, each hole being 8 feet deep and 2% inches in diameter. The blasting holes are spaced 2 feet apart. Explosive charges consisting of two sticks of a nitroglycerin sensitized semi-gelatin dynamite M; of an inch in diameter and 24 inches long and available commercially from Hercules Incorporated, and sold under the tradename Hercosplit WR are taped end to end on a single foot length of detonating cord. The detonating cord contains 50 grains per foot of PETN (pentaerythritol-tetranitrate) and is available commercially from the Ensign Bickford Company and is sold under the tradename Primacord". The free end of the detonating cord down-line of each of the holes is attached to a detonating cord trunk line. The end of the trunk line is connected to an electric blasting cap. Firing of the electric blasting cap initiates detonation of the trunk line and in turn the blasting charges in each of the blasting holes is detonated. The result is a good presplit crack.

The following example illustrates presplitting in accordance with this invention EXAMPLE 2 Example 1 is repeated employing blasting charges prepared from explosive charges having double lengths of detonating cord oriented 180 apart along the surface of the explosive charges said cords extending the length of the charges and being parallel with the longitudinal axis of each explosive charge as illustrated in FIGS. 1 and 2. The number of explosive charges and their position in the blast hole as measured from the surface of the rock formation into the blast hole is the same as employed in Example 1. The blasting charges are oriented in the blasting holes as illustrated in FIG. 4. The electric blasting cap is initiated and the blasting charge in each of the holes is detonated. The result is a good presplit crack.

Examples 3 and 4 which follow illustrate the results achieved when Examples 1 and 2 are repeated with the exception that the distance between blast holes in the blasting array is increased from 2 to 3 feet. Example 3 illustrates conventional presplitting. Example 4 illustrates the presplitting method of this invention.

EXAMPLE 3 Four holes are drilled in a straight line each hole being 8 feet deep and 2% inches in diameter. The holes are spaced 3 feet apart. The blasting charge employed is the same as in Example l. The free ends of the detonating cord down-lines are connected to a detonating cord trunk line. The end of the detonating cord trunk line is attached to a blasting cap. The blasting cap is initiated and the blasting charge in each hole is detonated. No presplit crack is produced. The detonation of the blasting charge in each hole rifled, i.e. the force from the detonation was principally directed through the open end of the blasting hole.

EXAMPLE 4 Example 3 is repeated. The blasting charge employed in each hole is the same as set forth in Example 2. The blasting charges are oriented within the hole as illustrated in FIG. 4. The free end of the detonating cord down-lines are joined to the detonating cord trunk lines. The detonating cord trunk line is initiated with an electrical blasting cap. The blasting charge in each hole is detonated and produces a good presplit crack.

Examples 5 and 6 which follow further illustrate comparitive results achieved in experiments employing conventional presplitting methods (Example 5) and the presplitting method of this invention (Example 6).

EXAMPLE 5 Example 3 is repeated in the same sector of rock formation but with the blast holes spaced four feet apart. The blasting charges of each hole rifle upon detonation. A presplit crack is not formed.

EXAMPLE 6 Example 5 is repeated in another set of blasting holes in the same sector of rock formation. The blasting charge employed and charge orientation is the same as employed in Examples 2 and 4. The blasting cap is initiated and the blasting charge in each blast hole is detonated. A good presplit crack results.

The foregoing examples illustrate the improved presplitting results that can be obtained when employing the Mach Effect for blasting in rock formations. Thus, the examples show that a suitable presplit crack can be obtained in a rock formation at a distance of 4 feet between blasting charges by orienting the blasting charge of this invention so that enhance force vector of each charge substantially coincides with the desired presplit line. By comparison with conventional presplitting methods a satisfactory presplit resulted only in the instance where the holes were spaced 2 feet apart.

In the foregoing description and examples, the positioning of the blasting charge within each blast hole and the configuration of the blasting charge is critical in order to achieve the Mach Effect in presplitting. Thus, in the most common application of presplitting, the desired presplit line will be straight. In this instance the charges are aligned so that a line joining the centers of the two detonating cords spaced apart about the surface of the blasting charge is perpendicular to the presplit line which can be drawn through the centers of the blast holes. When it is desired to presplit along an arc of a circle such as in tunneling, the blasting charges are positioned so that the force vectors which will result from detonation of each blasting charge substantially coincides with the presplit line desired. By the term substantially coincides with the presplit line.

The configuration of the blasting charge is critical in achieving the Mach Effect for presplitting. The blasting charge comprises an explosive charge in the form of a cylinder of explosive or in the form of two cylinders of explosive secured together in a contiguous relationship lengthwise of said cylinders; and two detonating cords secured to and disposed longitudinally on the surface of the explosive charge and parallel to the longitudinal axis thereof. The two detonating cords are spaced 180 apart on the surface of the explosive charge at the points on the surface of the explosive charge where a line passing through both the center of the explosive charge and the center(s) of the cylinder or two cylinders forming the explosive charge intersects the surface of the explosive charge. Where the explosive charge is simply a single cylinder of explosive, the center of the explosive charge and the center of t the cylinder forming the explosive charge are, of course, the

same.

In the presplitting method of this invention any explosive charge which is detonatable by the action of Primacord or the equivalent thereof can be employed. Illustrative explosive charges of this class include ammonia gelatins, ammonia semigel a tins and ammonia dynamites. Any of the above classes of explosive charges can be nitroglycerin sensitized. Other explosi ve charges that can be employed include nitrostarch sensitiz ed explosive compositions comprising ammonium nitrate, and optionally, nitrates of alkali and alkaline earth metals such assodium nitrate, potassium nitrate and barium nitrate, and one or more fuels including metal fuels and carbonaceous fuels. These explosive charges are contained within moisture resistant paper shells or shells of other suitable materials such as plastic or cellulosic materials. The explosive charges are employed in the form of cylinders.

Detonating cord is a strong flexible cord having a core containing anexplosive material. The cord itself can be prepared froma material suitable to meet the conditions encountered in actual ,use. Thus the cord can be prepared from textiles, plastics, and thelike. The explosive material within the core of the detonating material is preferably PETN (pentaerythritoltetranitrate) but other explosive materials capable of initiating the explosive charge such as cyclotrimethyenetrinitramine (RDX) can be employed. Detonating cord is readily secured to the surface of the explosive charges employed with tape, plastic clips, or channels fabricated in the explosive cartridge casing. Detonating cord forms the trunk line along which the detonation .shock travels at a very high velocity, say up to about 21,000 feet per second, to initiate the explosive charges within the blasting hole.

The detonating cord detonates when initiated by a suitable initiator means such as an electrical blasting cap. Electrical powercan be supplied to the electrically initiated blasting cap by any suitable circuit means said circuit means comprising for example a DC storage battery connected through a control means,.such as a switch, to the blasting cap.

The blasting system of this invention has been particularly described for use in presplitting of rock formations. This blasting system, however, has other uses and can be employed in applications wherein a linear shaped charge is used. The blasting system of this invention can be employed to establish a shear plane in rock, such as in the cutting of dimension stone.

What I claim and desire to protect by Letters Patent is:

1. A method of presplitting a rock formation comprising:

a. drilling a plurality of blasting holes along a desired presplit line,

b. charging each blasting hole with a blasting charge comprising an explosive charge, said explosive charge being in the form of a cylinder of explosive or two cylinders of explosive secured together in a contiguous relationship lengthwise of said cylinders, and two detonating cords, each detonating cord having a free end and a secured end, said secured ends being secured to and disposed longitudinally on the surface of the explosive charge parallel to the longitudinal axis of the explosive charge and spaced apart on the surface of the explosive charge at the points on the surface of the charge where a line passing through both the center of the explosive charge and the center(s) of the cylinder or cylinders forming the explosive charge intersects the surface of the explosive charge, the free ends of said detonating cords being connected to a detonation initiation means,

c. positioning the blasting charge within each blasting hole so that a high concentration of energy resulting from detonation of the blasting charge is focused so as to sub- ,7

stantially coincide with the desired presplit line, and

d. actuating the detonation initiation means whereby the detonating cords simultaneously detonate the explosive charge presplitting the rock formation.

2. The method of claim 1 wherein a plurality of explosive charges are each secured to, and spaced apart along the length of, the two detonating cords.

3. The method of claim 1 wherein the detonation initiation means comprises an electrically initiated blasting cap and an electrical supply circuit means for providing current to initiate said blasting cap.

4. The blasting method of claim 2 in which each of the explosive charges is in the shape of a cylinder and the detonating cords are secured to and disposed longitudinally on the surface of the cylindrical explosive charges parallel to the longitudinal axis of said explosive charge and spaced 180 apart.

5. The method of claim 4 wherein line plurality of blasting holes are drilled along a straight lone and each blasting charge is positioned within each blasting hole so that a line connecting the centers of the detonating cords of each blasting charge is perpendicular to the desired presplit line.

6. A blasting system employing the Mach Effect for presplitting said system having in combination:

a. blasting holes,

b. a blasting charge disposed in each blasting hole so that the energy resulting from detonation of the blasting charge is focused so as to substantially coincide with a desired presplit line, each blasting charge comprising an explosive charge, said explosive charge being in the form of a cylinder of explosive or two cylinders of explosive secured together in a contiguous relationship lengthwise of said cylinders, and two detonating cords, each detonating cord having a free end and a secured end, said secured ends being secured to and disposed longitudinally on the surface of the explosive charge parallel to the longitudinal axis of the explosive charge and spaced 180 apart on the surface of the explosive charge at the points on the surface of the charge where a line passing through both the center of the explosive charge and the center(s) of the cylinder or cylinders forming the explosive charge intersects the surface of the explosive charge, the free ends of said detonating cords being connected to a detonation initiation means,

c. means connected to the free ends of the two detonating cords of the blasting charge in each blasting hole for simultaneously detonating the two detonating cords of each blasting charge.

7. A blasting system employing the Mach Effect for presplitting said system having in combination:

a. blasting holes,

b. a blasting charge disposed in each blasting hole so that the energy resulting from detonation of the blasting charge is focused so as to substantially coincide with a desired presplit line, each blasting charge comprising an explosive charge, said explosive charge being in the form of a cylinder of explosive or two cylinders of explosive secured together in a contiguous relationship lengthwise of said cylinders, and two detonating cords, each detonating cord having a free end and a secured end, said secured ends being secured to and disposed longitudinally on the surface of the explosive charge parallel to the longitudinal axis of the explosive charge and spaced 180 apart on the surface of the explosive charge at the points on the surface of the charge where a line passing through both the center of the explosive charge and the center(s) of the cylinder or cylinders forming the explosive charge intersects the surface of the explosive charge, the free ends of said detonating cords being joined and connected to a detonating cord trunk line having a free end,

c. an electrically actuated detonator means connected to the free end of the trunk line,

d. electrical energy supply means, and

e. circuit means connecting the energy supply means to the electrically actuated detonator means when a control means is positioned conductive between the energy supply means and the electrically actuated detonator whereby the electrically actuated detonator means is detonated, detonating, in turn, the trunk line and the blasting charges. I

8. The method of claim 7 wherein a plurality of explosive charges are each secured to, and spaced apart along the length of, the two detonating cords.

9. The blasting method of claim 8 in which each of the explosive charges is in the shape of a cylinder and the detonating cords are secured to and disposed longitudinally on the surface of the cylindrical explosive charges parallel to the longitudinal axis of said explosive charge and spaced 180 apart.

10. A blasting system employing the Mach Effect for establishing a shear plane in rock said system having in combination:

a. blasting holes,

b. a blasting charge disposed in each blasting hole so that the energy resulting from detonation of the blasting charge is focuses so as to substantially coincide with a desired shear line, each blasting charge comprising an explosive charge, said explosive charge being in the form of a cylinder of explosive or two cylinders of explosive secured together in a contiguous relationship lengthwise of said cylinders, and two detonating cords, each detonating cord having a free end and a secured end, said secured ends being secured to and disposed longitudinally on the surface of the explosive charge parallel to the longitudinal axis of the explosive charge and spaced apart on the surface of the explosive charge at the points on the surface of the charge where a line passing through both the center of the explosive charge and the center(s) of the cylinder or cylinders forming the explosive charge intersects the surface of the explosive charge, the free ends of said detonating cords being connected to a detonation initiation means,

c. means connected to the free ends of the two detonating cords of the blasting charge in each blasting hole for simultaneously detonating the two detonating cords of each blasting charge. 

1. A method of presplitting a rock formation comprising: a. drilling a plurality of blasting holes along a desired presplit line, b. charging each blasting hole with a blasting charge comprising an explosive charge, said explosive charge being in the form of a cylinder of explosive or two cylinders of explosive secured together in a contiguous relationship lengthwise of said cylinders, and two detonating cords, each detonating cord having a free end and a secured end, said secured ends being secured to and disposed longitudinally on the surface of the explosive charge parallel to the longitudinal axis of the explosive charge and spaced 180* apart on the surface of the explosive charge at the points on the surface of the charge where a line passing through both the center of the explosive charge and the center(s) of the cylinder or cylinders forming the explosive charge intersects the surface of the explosive charge, the free ends of said detonating cords being connected to a detonation initiation means, c. positioning the blasting charge within each blasting hole so that a high concentration of energy resulting from detonation of the blasting charge is focused so as to substantially coincide with the desired presplit line, and d. actuating the detonation initiation means whereby the detonating cords simultaneously detonate the explosive charge presplitting the rock formation.
 2. The method of claim 1 wherein a plurality of explosive charges are each secured to, and spaced apart along the length of, the two detonating cords.
 3. The method of claim 1 wherein the detonation initiation means comprises an electrically initiated blasting cap and an electrical supply circuit means for providing current to initiate said blasting cap.
 4. The blasting method of claim 2 in which each of the explosIve charges is in the shape of a cylinder and the detonating cords are secured to and disposed longitudinally on the surface of the cylindrical explosive charges parallel to the longitudinal axis of said explosive charge and spaced 180* apart.
 5. The method of claim 4 wherein line plurality of blasting holes are drilled along a straight lone and each blasting charge is positioned within each blasting hole so that a line connecting the centers of the detonating cords of each blasting charge is perpendicular to the desired presplit line.
 6. A blasting system employing the Mach Effect for presplitting said system having in combination: a. blasting holes, b. a blasting charge disposed in each blasting hole so that the energy resulting from detonation of the blasting charge is focused so as to substantially coincide with a desired presplit line, each blasting charge comprising an explosive charge, said explosive charge being in the form of a cylinder of explosive or two cylinders of explosive secured together in a contiguous relationship lengthwise of said cylinders, and two detonating cords, each detonating cord having a free end and a secured end, said secured ends being secured to and disposed longitudinally on the surface of the explosive charge parallel to the longitudinal axis of the explosive charge and spaced 180* apart on the surface of the explosive charge at the points on the surface of the charge where a line passing through both the center of the explosive charge and the center(s) of the cylinder or cylinders forming the explosive charge intersects the surface of the explosive charge, the free ends of said detonating cords being connected to a detonation initiation means, c. means connected to the free ends of the two detonating cords of the blasting charge in each blasting hole for simultaneously detonating the two detonating cords of each blasting charge.
 7. A blasting system employing the Mach Effect for presplitting said system having in combination: a. blasting holes, b. a blasting charge disposed in each blasting hole so that the energy resulting from detonation of the blasting charge is focused so as to substantially coincide with a desired presplit line, each blasting charge comprising an explosive charge, said explosive charge being in the form of a cylinder of explosive or two cylinders of explosive secured together in a contiguous relationship lengthwise of said cylinders, and two detonating cords, each detonating cord having a free end and a secured end, said secured ends being secured to and disposed longitudinally on the surface of the explosive charge parallel to the longitudinal axis of the explosive charge and spaced 180* apart on the surface of the explosive charge at the points on the surface of the charge where a line passing through both the center of the explosive charge and the center(s) of the cylinder or cylinders forming the explosive charge intersects the surface of the explosive charge, the free ends of said detonating cords being joined and connected to a detonating cord trunk line having a free end, c. an electrically actuated detonator means connected to the free end of the trunk line, d. electrical energy supply means, and e. circuit means connecting the energy supply means to the electrically actuated detonator means when a control means is positioned conductive between the energy supply means and the electrically actuated detonator whereby the electrically actuated detonator means is detonated, detonating, in turn, the trunk line and the blasting charges.
 8. The method of claim 7 wherein a plurality of explosive charges are each secured to, and spaced apart along the length of, the two detonating cords.
 9. The blasting method of claim 8 in which each of the explosive charges is in the shape of a cylinder and the detonating cords are secured to and disposed longitudinally on the surface of the cylindrical explosive charges parallel to the lOngitudinal axis of said explosive charge and spaced 180* apart.
 10. A blasting system employing the Mach Effect for establishing a shear plane in rock said system having in combination: a. blasting holes, b. a blasting charge disposed in each blasting hole so that the energy resulting from detonation of the blasting charge is focuses so as to substantially coincide with a desired shear line, each blasting charge comprising an explosive charge, said explosive charge being in the form of a cylinder of explosive or two cylinders of explosive secured together in a contiguous relationship lengthwise of said cylinders, and two detonating cords, each detonating cord having a free end and a secured end, said secured ends being secured to and disposed longitudinally on the surface of the explosive charge parallel to the longitudinal axis of the explosive charge and spaced 180* apart on the surface of the explosive charge at the points on the surface of the charge where a line passing through both the center of the explosive charge and the center(s) of the cylinder or cylinders forming the explosive charge intersects the surface of the explosive charge, the free ends of said detonating cords being connected to a detonation initiation means, c. means connected to the free ends of the two detonating cords of the blasting charge in each blasting hole for simultaneously detonating the two detonating cords of each blasting charge. 